Method and apparatus for sport swing analysis system

ABSTRACT

A sports swing implement is coupled to reflective material in order to enhance the detection properties of the implement as it is swung.

This application is a continuation of United States Patent Applicationhaving Ser. No. 09/952,714, entitled, “SPORT SWING ANALYSIS SYSETM,”which is hereby incorporated by reference in its entirety. The presentapplication has the same inventors as, is assigned to the same entityas, and claims benefit of the same filing date, Sep. 14, 2001, as thisapplication. Applications having the same inventors, the same assignee,and docket numbers: GT1CONTA, GT1CONTB, GT1CONTC, GT1CONTD, GT1CONTE,GT1CONTF, GT1CONTG, GT1CONTH, GT1CONTI, and GT1CONTJ are being filed onthe same day herewith and each incorporates the other by reference.

FIELD OF THE INVENTION

The present invention relates to systems and methods to aid in analyzingthe swing associated with athletic activities. More particularly, thepresent invention relates to a system and method for detecting andanalyzing the path and orientation of an sports implement, such as agolf club, as it is swung. Although the present invention is well suitedto the analysis of a golf club's swing, its application is not limitedthereto.

BACKGROUND OF THE INVENTION

Practice makes perfect. However hackneyed that bromide may be, it offersan element of truth. That is, the skill-level of an individual,particularly in those tasks that involve muscle-memory, such as athleticor musical-performance activities, is directly related to the number ofquality hours spent engaged in those pursuits. Pete Maravich almostalways had his hands on a basketball, Jimi Hendrix rarely set his guitardown; even those with great natural ability developed their talentsthrough many, many hours of practice. The implication of the term“quality hours” is that the time must be spent in a manner that providesfeedback to allow the practitioner to modify his execution in order toimprove his performance. A “sour note” in a blues riff, a concussionincurred while attempting a double back flip off a high board, or a hookinto the rough off a golf tee are all forms of feedback that provide alearning opportunity to an aspiring competitor/performer.

There are a number of sports activities that involve extraordinarilycomplex swinging movements. The fact that no major league player has hit0.400 since Ted Williams did so in his 1941 season is a testament to theextreme difficulty of effectively swinging a baseball bat. A sixtypercent failure rate would be disastrous in nearly any other endeavor,but, in baseball, it's the apex of performance. Similarly, the manymechanical degrees of freedom associated with a golf swing conspire toprovide the average duffer with many opportunities for failure and themechanics of swinging a tennis racquet are critical to success in thatsport. Ice hockey, field hockey, and lacrosse are among the other sportactivities that rely upon the skillful swing of an implement (that is, abat, a club, a racquet, etc.). Although professionals are available tohelp athletes improve their swings (e.g., hitting coaches for baseballplayers and golf and tennis professionals), costs associated with suchlessons are beyond the means of the vast majority of players. Schedulingthe time for and traveling to lessons adds another layer ofinconvenience to this approach for improving your golf game.Additionally, athletic activities involving the use of an implementmoving at a high rate of speed, it can be difficult to accurately assessany flaws in the mechanics of an individual's swing.

Devices and systems are available for sport participants to makecritical evaluations of the techniques and mechanics associated withtheir sport of interest. In the sport of golf there have been a numberof advances in golf club swing analysis. For example, U.S. Pat. No.5,718,639 issued to Bouton, U.S. Pat. No. 5,474,298 issued to Lindsay,and U.S. Pat. No. 6,227,984 issued to Blankenship, disclose variousapproaches to sensing and analyzing golf swings. Notwithstanding theabundance of swing analysis systems, the development of accurate,inexpensive swing sensing and analysis systems remains elusive.

An automated system that analyzes a sport swing and provides feedback toa player as a convenient, accurate, low-cost alternative to theengagement of coaches and/or professionals would be highly desirable.

SUMMARY

A sport swing analysis system and method in accordance with theprinciples of the present invention senses electromagnetic energyreflected from a sports implement. The reflected energy may be of anywavelength or band of wavelengths. Although the wavelength of the energymay fall outside the range referred to as the visual spectrum, theenergy will be referred to hereinafter as “light.” For the purpose ofillustration, examples of operation using infrared light will beemployed.

A system and method in accordance with the principles of the presentinvention emits light then detects light reflected from a sportsimplement, such as a golf club, baseball bat, or tennis racquet, forexample. As the sports implement passes by one or more of photo-emitters(emitters) the implement reflects a portion of the light striking itfrom the emitters. One or more photo-detectors (detectors) detect lightreflected from the implement and the amplitude of light reflected intoone or more of the detectors will vary with the passing of theimplement.

In accordance with the principles of the present invention, the systemmay employ pattern recognition methods and apparatus, including, but notlimited to, edge detection techniques, to distinguish the lightreflected from the implement and received at the detector(s) frombackground light and light from other sources that is received at thedetector(s). Light from outside sources, also referred to herein as“artifact,” is a potential source of error and, once identified, isignored by the system. In an illustrative embodiment, the edge-detectionprocess includes the step of differentiating a swung sports implement'sreflection profile to determine one or more points of inflection in theprofile. The one or more points of inflection correspond to relativelysharp transitions in the amplitude of reflected light, and correspond toone or more identifiable features on the swung implement. Eachidentifiable feature may, for example, be a transition between materialshaving relatively high light absorption and relatively high lightreflectivity. In an illustrative embodiment, the system storesinformation related to each such light level transition that meets athreshold criteria. Such information may include the time at which thetransition occurred (that is, a time stamp) and a “tag” that identifiesthe detector that detected the light-level transition.

In an illustrative example, the identifiable features may be the leadingand trailing edges of a reflective strip coupled to the swung implement.The reflective strip may be coupled to the implement using anyattachment means, including, but not limited to, adhesives, hook andloop, tying, or strapping, for example. Alternatively, the reflectivematerial may be integral with the swung implement, with one or morestrips of reflective material embedded within the head of a golf club,within the body of a baseball bat, or within the head of a tennisracquet, for example. The reflective strip may, additionally, be flankedby one or more regions of highly light-absorptive material in order toestablish a high-contrast reflectivity region: that is, a region inwhich the material surfaces present an abrupt shift from highlylight-absorptive to highly light-reflective. Such a high-contrastreflectivity region enhances the system's ability to detect reflectiontransition events, thereby allowing the system to more preciselydetermine the exact time and location of transition events. For example,in an illustrative embodiment, a highly absorptive material, such asblack electrical tape, is applied to the bottom surface of a golf club'shead, then a strip of retroreflective material, is attached, viaadhesive backing, to the absorptive material (that is, the black tape),with some of the absorptive material left uncovered. The combination ofabsorptive material and overlaid reflective material yieldshigh-contrast reflectivity regions at the leading and trailing edges ofthe strip.

In another aspect of a system in accordance with the principles of thepresent invention, the retroreflective strip is of a known width and isaligned with leading and trailing edges parallel to the face of theclub. An alignment tool may be employed to ensure that the strip isproperly aligned with the face of the club. Knowing the width of thereflective strip allows the system to determine the speed of theassociated swung implement by dividing the width of the strip by thetime between reflectivity transitions associated with the leading andtrailing edges of the reflective strip.

Triangulation techniques may be employed by a system in accordance withthe principles of the present invention to determine the distancebetween the implement and the system's light detectors. In anillustrative golf club swing analysis embodiment, such a distancemeasurement may be used to provide an indication of the height of aswung club head above a surface holding the golf ball. Such a golf clubswing analysis embodiment may include one or more arrays of detectorsand emitters) embedded in a housing that provides support for a golfball on its upper surface. The emitters and detectors are coupled to acontroller that controls the output of the emitters and samples theinput to the detectors. The controller may also perform signalconditioning, the timestamping, amplitude profile creation, and edgedetection processes discussed briefly above, or, alternatively, mayoffload some, or all, of these tasks to an associated computer. Thetasks associated with a swing analysis system in accordance with theprinciples of the present invention may be divided between thecontroller and a computer in a number of ways. In an illustrativeembodiment, the amplitude profile stored includes the identification ofthe detector that experienced the light transition, the direction of thetransition (that is, going from dark to light, or going from light todark), and the time of the transition. However those tasks are divided,the system may be used to determine and display swing path angle, clubhead speed, club head angle, club head lateral alignment with respect toa ball support, club head loft angle, and club head height.Additionally, the system may be employed to calculate and display an“effective club head speed,” which takes into account the raw speed ofthe club head and discounts that speed according to swing path angle,club head lateral alignment, and club head angle. Sensor arrays (thatis, arrays of emitters and detectors) are positioned within andsupported by a sensor housing in a manner that permits the sensors todetect and analyze the passage of a swung club before, after, and at thepoint of impact with a ball.

A swing analysis system in accordance with the principles of the presentinvention may analyze slower motioned swings, such as putting strokes ina golf swing analysis embodiment and may incorporate both “regular”swing analysis (that is, the analysis of swings other than puttingstrokes) and putting swing analysis into one or more practice modes andinto one or more game modes.

The system may include a user interface the provides a variety oftextual and graphical information related to swing analysis and mayinclude views of a struck ball's trajectory including, “still”, “followthe ball”, and “spin” views. In the “still” view, the user observes theball trajectory from a stationary viewpoint corresponding to the placewhere he was standing when he hit the ball. In the “follow the ball”view, the user's viewpoint follows the ball, as thought tethered to theball. In the “spin” view, the viewpoint follows the ball and then spinsto a side view that travels along with the ball.

An applicator that properly aligns reflective material on the implementthat is to be swung for analysis is also contemplated within the scopeof the invention, as is a mat that is configured to receive a sensorhousing and to support a user at approximately the same level as the topof the sensor housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further features, aspects, and advantages of the inventionwill be apparent to those skilled in the art from the following detaileddescription, taken together with the accompanying drawings in which:

FIG. 1 a is a conceptual block diagram of a sports swing analysis systemin accordance with the principles of the present invention and FIGS. 1b, 1 c, and 1 d depict a baseball bat, a tennis racquet, and a golf clubcoupled to retroreflective materials in accordance with the principlesof the present invention;

FIG. 2 is a perspective view of a golf swing analyzer system inaccordance with the principles of the present invention;

FIGS. 3 a through 3 h illustrate the application of retroreflectivematerials to a golf FIG. 4 is a top plan view of a golf swing analyzersensor housing in accordance club head in accordance with the principlesof the present invention; with the principles of the present invention;

FIGS. 5 a through 5 b illustrate in greater detail the operation of agolf swing analyzer in combination with retroreflective materials inaccordance with the principles of the present invention;

FIG. 6 is a block diagram of a sensor system in accordance with theprinciples of the present invention;

FIG. 7 is a block diagram of a computer such as may be used inimplementing a sports swing analysis system in accordance with theprinciples of the present invention;

FIG. 8 is a flow chart of the process of sports swing analysis inaccordance with the principles of the present invention;

FIG. 9 is a screen shot of a sports swing analysis system in accordancewith the principles of the present invention in which display componentsrelated to a golf swing are illustrated;

FIG. 10 is a screen shot of a sports swing analysis system in accordancewith the principles of the present invention in which display componentsrelated to a golf putting swing are illustrated;

FIG. 11 is a screen shot of a sports swing analysis system in accordancewith the principles of the present invention in which display componentsrelated to a golf course layout are illustrated; and

FIGS. 12 a and 12 b are, respectively, perspective and end views of agolf mat such as may be employed by a sports swing analysis system inaccordance with the principles of the present invention.

DETAILED DESCRIPTION

A sports swing analysis system in accordance with the principles of thepresent invention may be configured and employed to analyze thecharacteristics of a swung sports implement. Although the implementcould be any of a number of sports implements that are swung during thecourse of a sports activity, such as a baseball bat, a tennis racquet, ahockey stick, or a golf club, the following description willconcentrate, for the sake of brevity and clarity of exposition, on thedetection and analysis of a golf swing, in the details.

The conceptual block diagram of FIG. 1 a outlines three functionalbuilding blocks of a sports swing analysis system 100 in accordance withthe principles of the present invention. The detection systems 102interface with signal generation and processing functions 104 that, inturn, interface with analysis, control, and user interface functions106. The functions represented in the blocks 102, 104, and 106 may bedistributed in a number of ways; with the functions dispersed in aplurality of packages or with all the functions located within a singlepackage. As will be described in greater detail in the discussionsrelated to subsequent Figures, in an illustrative embodiment of a golfswing analysis system, the majority of the detection system 102 andsignal generation and processing 104 functions are located within asensor housing that is linked with a general purpose computer upon whichhave been coded the analysis, control, and user interface functions 106.

The detection system functions 102, as described in greater detail inthe discussion related to the following Figures, include the placementand orientation of electromagnetic emitters and detectors and the use ofretroreflective materials to optimize the operation of the emitters anddetectors. Although the electromagnetic energy employed by thephotoemitters (emitters) and photodetectors (detectors) may be of anywavelength or band of wavelengths, and the wavelength(s) of the energymay fall outside the range referred to as the visual spectrum, theenergy will be referred to hereinafter as “light.” For the ease andclarity of illustration, examples of operation using infrared light willbe employed.

A system and method in accordance with the principles of the presentinvention emits light then detects light reflected from a sportsimplement, such as a golf club, baseball bat, or tennis racquet, forexample. As the sports implement passes by one or more of photo-emitters(emitters) the implement reflects a portion of the light striking itfrom the emitters. One or more photo-detectors (detectors) detect lightreflected from the implement and the amplitude of light reflected intoone or more of the detectors will vary with the passing of theimplement.

In accordance with the principles of the present invention, the systemmay employ pattern recognition methods and apparatus, including, but notlimited to, edge detection techniques, to distinguish the lightreflected from the implement and received at the detector(s) frombackground light and light from other sources that is received at thedetector(s). Light from outside sources, also referred to herein as“artifact,” is a potential source of error and, once identified, isignored by the system. In an illustrative embodiment, the edge-detectionprocess includes the step of differentiating a swung sports implement'sreflection profile to determine one or more points of inflection in theprofile. The one or more points of inflection correspond to relativelysharp transitions in the amplitude of reflected light, and correspond toone or more identifiable features on the swung implement. Eachidentifiable feature may, for example, be a transition between materialshaving relatively high light absorption and relatively high lightreflectivity. In an illustrative embodiment, the system storesinformation related to each such light level transition that meets athreshold criteria. Such information may include the time at which thetransition occurred (that is, a time stamp) and a “tag” that identifiesthe detector that detected the light-level transition.

In an illustrative example, the identifiable features may be the leadingand trailing edges of a reflective strip coupled to the swung implement.The reflective strip may be coupled to the implement using anyattachment means, including, but not limited to, adhesives, hook andloop, tying, or strapping, for example. Alternatively, the reflectivematerial may be integral with the swung implement, with one or morestrips of reflective material embedded within the head of a golf club,within the body of a baseball bat, or within the head of a tennisracquet, for example. The reflective strip may, additionally, be flankedby one or more regions of highly light-absorptive material in order toestablish a high-contrast reflectivity region: that is, a region inwhich the material surfaces present an abrupt shift from highlylight-absorptive to highly light-reflective. Such a high-contrastreflectivity region enhances the system's ability to detect reflectiontransition events, thereby allowing the system to more preciselydetermine the exact time and location of transition events.

For example, in an illustrative embodiment, a highly absorptivematerial, such as black electrical tape, is applied to the bottomsurface of a golf club's head, then a strip of retroreflective material,is attached, via adhesive backing, to the absorptive material (that is,the black tape), with some of the absorptive material left uncovered.The combination of absorptive material and overlaid reflective materialyields high-contrast reflectivity regions at the leading and trailingedges of the strip. FIG. 1 b illustrates a baseball bat 108 having aplurality of reflective strips 110 attached to the tip of the bat 108over highly light-absorbent material 112. FIG. 1 c illustrates a tennisracquet 114 having a reflective strip 116 attached to the racket over ahighly light-absorbent material 118. FIG. 1 d illustrates a golf club210 having a reflective strip attached to the club over a highlylight-absorbent material 213. The placement of the reflective strip andlight absorbent material for all the implements may vary withapplication.

The signal generation and processing functions 104, as described ingreater detail in the discussion related to the following Figures,include the use of pattern detection techniques and the timed activationof the emitters. The analysis, control, and user interface functions106, described in greater detail in the discussion related to thefollowing Figures, include the analysis of a swung implement, display ofa simulated result of the swing, and audio and/or graphical feedbackrelated to the analysis of the swing.

An illustrative embodiment of a golf swing analysis system 200 inaccordance with the principles of the present invention is shown in theperspective view of FIG. 2. The system 200 include a sensor housing 202or equivalent structure for containing therein a plurality emitters anddetectors. As will be described in greater detail in the discussionrelated to the following Figures, the emitters and detectors arearranged into six groups, or arrays, identified in the Figures byreference numerals 204 a, 204 b, 204 c, 204 d, 204 e, and 204 f. Thesystem 200 further includes signal generation and processing components206 contained, in this illustrative embodiment, within the housing 202.As described in greater detail in the discussion related to thefollowing Figures, the signal generation and processing components arecoupled to the emitters and detectors (204 a-204 f) and to a generalpurpose computer 208.

A golf club 210 having retroreflective material 212 coupled to it isswung by a user over the housing 202 in order to capture data foranalysis of the user's golf swing, and for providing various forms offeedback to the user by the system 200. A mat 215 may be employed toprovide a level, resilient, grass-like surface upon which a user maystand. The mat 215 simulates the look and feel of a golf course surfaceand, with a thickness approximately the same as the thickness of thehousing 202, positions a user level with the upper surface 202 a of thehousing 202. The illustrative system 200 also includes a net 214 whichmay be positioned to capture golf balls hit by a user.

Retroreflective material, such as used in this illustrative embodiment,is familiar to most people through its use in traffic signs. Thematerial provides the unique property of returning light to a lightsource, rather than, as with conventional reflective material,reflecting light according to the familiar, “angle of incidence equalsthe angle of reflection,” rule. Retroreflective materials are typicallyone of two types: enclosed-lens, glass bead sheeting, or microprismatic,“cube-corner,” reflective material. “Glass bead” sheeting features acomplex construction of many laminated layers. Thousands of microscopicglass beads are embedded per square inch in these layers. Sandwichedbetween the adhesive and bead layers, a metalization layer is closelymolded to the contoured backside of the beads, and acts as a reflector.Light passes through the film's top layers and strikes this layer.Bouncing off the metalization layer, light returns through the beadsback through to the light source. Microprismatic retroreflectivematerial uses an embossed geometric pattern on the sheeting's interiorsurface to refract the light beam. By bouncing the light off differentplanes of the pattern, the light is redirected back to its origin.Various retroreflective film types are available from manufacturers,such as 3M corporation, Saint Paul, Minn.

The illustrative sensor housing 202 may be fabricated of a resilientmaterial, with the emitters and detectors (204 a-204 f) embeddedtherein. In this illustrative embodiment, the emitters and detectors arereflective type sensors wherein the detectors produce a signalproportional to the amplitude of light they detect of the wavelengthemitted by the emitters. Typically, background radiation will contributeto a signal at one or more of the detectors, but, as described ingreater detail in the discussion related to the following Figures, thesystem 200 employs signal processing techniques to eliminate the effectsof such “artifact.” This illustrative embodiment employs QED123 andQSD123 emitters and detectors, respectively, available from FairchildSemiconductors. The housing 202 is primarily composed of opaquematerial, with ports formed in the upper surface 202 a of the housing202 at the locations of the sensors 204 a-204 f. In this illustrativeembodiment, each of the sensors may be thought of as an emitter/detectorpair. Emitters within a group of sensors will be referenced by theaddition of an “e” to the respective sensor's reference number, anddetectors will be referenced by the addition of a “d” to the respectivesensor's reference number. For example, emitters within the 204 a sensorgroup will be associated with reference numeral 204 ae and, similarly,detectors within the 204 a sensor group will be associated with thereference numeral 204 ad. The ports may be open or covered by aresilient material, such as Plexiglas, that does not substantiallyabsorb light at the wavelength employed by the sensors. In use, thehousing 202 is positioned such that when a golf club 210 is swung, thehead of the golf club 210 travels along a swing path 216 that passesover the housing upper surface 202 a. Specifically, the swing path 216passes over the housing back edge 202 b, one or more of the sensors (204a-204 f), and then the housing front edge 202 c. A ball support 205 willdirectly support a golf ball substantially at the level of the housingupper surface 202 a, to simulate the positioning of a ball while puttingor, in general, during any shot other than a tee shot. Additionally, theball support 205 is configured to accept a golf tee and to therebypermit a golfer to take a tee shot.

In this illustrative embodiment, the emitters and detectors of sensors204 a-204 f respectively emit and accept relatively narrow beams ofinfrared light. As described in greater detail in the discussion relatedto the following Figures, the properties of the reflective material 212coupled to the head of the club 210 permit the use of relatively narrowbeams, which, in turn, provides greater accuracy in detecting thepresence or absence of the head of a club 210 above the housing 202. Inthe illustrative embodiment, the emitted light forms a beam with aspread of approximately +/−11 degrees. The detectors are sensitive overa comparably narrow range. Such as narrow beam allows the system todistinguish smaller features over a greater distance than otherwisewould be the case. Consequently, the accuracy and resolution of thesystem is increased concomitantly. With a conventional reflectivesurface, the reflected energy would only activate the detectors if thereflecting surface were substantially perpendicular to the central beamof the incident light energy. Additionally, a change in orientationrelative to horizontal would appear as a horizontal shift in position ifa conventional reflective surface were employed. In this illustrativeembodiment, the reflective material 212 is a retroreflective tape thatis applied to the bottom of the head of the club 210. The process ofapplying the retroreflective tape, along with a material 213 that ishighly absorbent in the wavelength or band of wavelengths used by thesensors 204 a-204 f, is described in greater detail in the discussionrelated to FIGS. 3 a through 3 j.

In operation, light transmitted by an emitter only returns to a nearby,associated, detector when it is reflected by an object, such as theretroreflective tape 212. As a club 210 is swung along the swing path216, light from one or more of the emitters 204 ae-204 fe is reflectedback to one or more of the detectors 204 ad-204 fd by the reflectivestrip. Additionally, light from the emitters 204 ae-204 fe issubstantially absorbed before and after passage of the reflective strip212 by the absorbent material 213 which, in this illustrative example,substantially surrounds the reflective strip 212. The contrast betweenhigh levels of absorption and high levels of reflectivity provides for asharp transition in reflected light amplitude that a system inaccordance with the principles of the present invention may use toclearly distinguish the passage of a club head from fluctuations inlight amplitude not due to the passage of a club head and, therefore,not relevant to a sports swing analysis system. Not only does the sharpcontrast provided by the combination of absorbent and reflectivematerials distinguish such background fluctuations from light amplitudetransitions of interest, it also allows the system 200 to determine withsome precision the exact time at which the edge of the retroreflectivematerial passes over a sensor and, therefore, permits the system to moreaccurately determine the values of swing parameters of interest, suchas: swing path angle, club head speed, club head angle, club headlateral alignment with respect to a ball support, club head loft angle,and club head height.

The array of sensors 204 a operate as triggers. That is, power isconstantly applied to the emitters and detectors so that the sensors maydetect the passage of a club head at any time. When a trigger event isdetected by sensors in the trigger row 204 a, the remaining sensors, inparticular the emitters of the remaining sensors, are turned on at fullpower for a period of time that is sufficient to capture swing data.Contact row sensors 204 d are positioned in close enough proximity to aball support 205 to obtain club head data approximately at the time ofthe club's impact with a ball. That is, the trailing edge of a properlyplaced reflective strip will be detected substantially coincident withthe striking of the ball. Sensor arrays 204 c and 204 e are used toevaluate club head toe and club head heel height before and after thepoint of impact, which provides further information on how the ball isstruck relative to the sweet spot of the club head face. Club head toeand heel height are determined using a technique that is a variation onstandard triangulation for distance determination. In an illustrativeembodiment, the sensors are angled approximately 30 degrees with respectto a line perpendicular to the upper surface of the housing 202 a.However, it will be understood that the sensors could be oriented at anyreasonable angle, for example, from 15 degrees to 75 degrees. Note that,without the retroreflective surface, the angled beams would not activatetheir respective detectors. Since each of the sensors arrays 204 c and204 e include two parallel rows (204 cl and 204 cr, and 204 el and 204er, respectively) effectively situated an equal distance on either sideof the tee, for a right handed golfer swinging in the directionindicated by the path 216, the height of the toe of the club is measuredby sensor rows 204 cr and 204 er, and the height of the heel of the clubis measured by sensor rows 204 cl and 204 el. This configuration enablesthe club head toe and heel heights to be measured independently, which,in turn, enables the system to provide a more accurate depiction of theswing, as is described below. The operation of entrance row sensors 204b, exit row sensors 204 f and angled sensors 204 c and 204 e will bedescribed in greater detail below.

The ball support 205 may directly support a ball, for example, when agolfer is operating the system in a putting mode, or, with the insertionof a tee into the hole 207 within the ball support by a golfer, the ballsupport 205 may support a tee which, in turn, supports the ball. Theoutput of the entrance row 204 b and exit row 204 f sensors is used todetermine the club's swing path angle and the club head's lateralalignment with the ball. The system employs a combination of parametervalues, including: swing path angle, lateral alignment, and face angle,to indicate whether the ball has been struck on the center of the clubhead face (that is, the sweet spot) or if the ball has been struck onthe heel or toe of the club head.

In accordance with the principles of the present invention, a distancemeasurement device 211 may be employed to determine the launch angle ofa golf ball after a user strikes the ball. The distance measurementdevice 211 may be based on any of a variety of known technologies, suchas RADAR or LIDAR, for example. In operation, the distance measurementdevice is located a known distance D4 from the ball support 205. Giventhe known distance D4, the distance measurement obtained by the device211 may be used by the system to determine a golf ball's launch angle(that is, the vertical angle of the ball as it leaves the ball support).In a relatively simple embodiment, one or more of the devices 211 arepositioned down range of the ball support forming a line perpendicularto the intended flight path of the ball at the distance D4 from the ballsupport. As a struck ball passes over one of the distance measurementdevices 211, the device measures the vertical distance to the ball H(that is, the ball's height) and reports this information to acontroller 600 (see FIG. 6). Given the ball's height and the distance D4to the ball support, the controller or computer can determine the launchangle as the arctangent of H/D4. This approach assumes that the heightmeasurement is obtained as the ball passes directly over the device 211and, therefore, the angle between the line from the device 211 to theball and the line from the ball support 205 to the device 211 is a rightangle.

Other configurations are contemplated within the scope of the invention.For example, in another illustrative embodiment, the device 211 is aRADAR device that employs phased-array techniques to steer a radar beamin order to determine the distance to a struck ball from the device.Phased arrays and RADAR beam steering is known in the art and compact,steerable, inexpensive RADAR systems are known. A compact, inexpensive,steerable, RADAR is disclosed, for example in, “A Fully Integrated24-Ghz 8-path Phased Array Receiver in Silicon”, Hossein Hashemi, XiangGuan, and Ali Hamjimiri, International Solid State Circuits Conference,2004, which is hereby incorporated by reference in its entirety. Asystem in accordance with the principles of the present invention mayemploy a steerable RADAR to obtain a variety of measurements, includingthe height and distance to a ball. Such measurements may be made one ormore times. Because such a RADAR device may be used to determine boththe distance and direction to a struck ball, the device may be locatedanywhere within a range of interest (that is, close enough to aprojected ball flight path to obtain measurements), and wouldn't need tobe positioned down range from the ball support 205. In order totransform angle and distance measurements from the device's coordinatesystem to that of the ball support and to thereby derive suchmeasurements as ball launch angle, the RADAR device's position relativeto that of the ball support must be determined. In order to simplify thecoordinate transformation, a RADAR device may be positioned apredetermined distance D4 down range from the ball support, along acenter line that travels through the center of the ball support 205 inthe direction of the expected ball flight path. Readings obtained whenthe ball is directly overhead provide a direct measure of a ball'sheight and the ball's launch angle is given, as described above, by thearctangent of H/D4. Vector decomposition may be used to determine theheight and directional angle (the angle, for example, to the left or theright of the center line) of a ball by transforming the height and angleof a ball in the receiver's coordinate system to the height and angle ofthe ball in the ball support's coordinate system. In accordance with theprinciples of the present invention a steerable RADAR device 211 mayalso be employed to make club head measurements, such as club headheight, speed, path, etc.

In another aspect of a system in accordance with the principles of thepresent invention, the retroreflective strip is of a known width and isaligned with leading and trailing edges parallel to the face of theclub. Additionally, an alignment tool may be employed to ensure that thestrip is properly aligned with the face of the club. Knowing the widthof the reflective strip allows the system to determine the speed of theassociated swung implement by dividing the width of the strip by thetime between reflectivity transition events associated with the leadingand trailing edges of the reflective strip. Triangulation techniques maybe employed by a system in accordance with the principles of the presentinvention to determine the distance between the implement and thesystem's light detectors. In an illustrative golf club swing analysisembodiment, such a distance measurement may be used to provide anindication of the height of a swung club head above a surface holdingthe golf ball.

FIGS. 3 a through 3 f provide illustrative examples of light-absorbentand light-reflective material such as may be used in accordance with theprinciples of the present invention and their application to the head ofa golf club, such as golf club 210. FIG. 3 a is a bottom plan view of agolf club head 300 having fore (or face) 302, aft 304, and bottom 306surfaces. The face 302 strikes the ball, ideally, in a manner thatprovides preferred characteristics, such as height, distance, direction,and other characteristics discussed in greater detail in the discussionrelated to the following Figures. In order to properly measureparameters such as club head speed, loft, club face angle and club pathangle, the systems sensors 204 a-204 f must detect the actualorientation of the club head as it is swung along the path 216. Becausethe reflectivity of a club head varies, because of a club head'scurvature, and because these and other club head characteristicsdifferfrom club to club, it is difficult to determine, with a great dealof precision, the actual orientation and speed of a club head simply byrelying upon light reflected from the club head into one or more arraysof detectors. In accordance with the principles of the presentinvention, the use of a retroreflective strip minimizes theuncertainties associated with the use of light reflected directly from aclub head and thereby allows for precise determination of club headspeed and orientation. Although a system in accordance with theprinciples of the present invention could operate successfully with areflective strip having any orientation relative to the club face 302,as long as the orientation was known, in this illustrative embodimentthe long axis of the reflective strip is oriented parallel to the faceof the club. By orienting the reflective strip in this manner, thesystem needn't transform data between a club face-centered coordinatesystem and a reflective strip-centered coordinate system. An alignmenttool 307 in accordance with the principles of the present invention maybe employed to ensure that the strip 212 is aligned parallel to the clubface and with the sweet spot of the club face. FIG. 3 b includesretroreflective strips 212, light absorbing material in the form ofblack electrical tape 213, and a reflective strip alignment tool 307.FIG. 3 c illustrates the bottom surface of a club head with blackelectrical tape 213 applied in accordance with the principles of thepresent invention.

FIG. 3 h illustrates an alignment tool in accordance with the principlesof the present invention in greater detail. The applicator 307, which,in this illustrative embodiment is composed of a pliable, resilient,material such as polystyrene or polypropylene, includes a substantiallyrectangular member 310 having an aperture 312 for accepting a reflectivestrip that is to be applied to a club head 211. One or more tabs 314 areconnected to the member 310 via a pliable joint 316, which joint may becreated by forming a weakened line of material. The “weakened line” maybe achieved by thinning the material, for example. Although two tabs areshown in this illustrative embodiment, any number of tabs, including asingle tab running the entire length of the rectangular member, may beemployed in accordance with the principles of the present invention. Inoperation, the tabs 314 are bent along the face of the club 302, asillustrated in FIG. 3 e, centered on the club face's sweet spot. Theaperture 312 is thereby positioned over the applied absorbent surface213, with its long axis aligned with the club face 302. Although theretroreflective material may be coupled to a club head through anymeans, including semiperminant means, such as molding, soldering, etc.,the use of retroreflective tape allows a golfer to apply the material toclubs he already owns and uses for playing golf.

FIG. 3 f illustrates the application of a reflective strip 212 to theabsorbent surface 213. In this illustrative embodiment the reflectivestrip 212 includes a retroreflective surface with an adhesive backing.The strip's adhesive backing is exposed before placing the strip withinthe aperture 312 and, consequently, when firmly positioned within theaperture 312, the strip adheres to the absorbent material 213 andremains affixed to the material 213 when the applicator 307 is removed,as illustrated in FIG. 3G.

FIG. 4 provides a more detailed view of a golf swing analysis systemsensor housing 200 in accordance with the principles of the presentinvention. Sensors are arranged within the housing as follows. Sensors204 a are positioned at the trigger row of the housing. The sensors 204a include three emitter/detector pairs. One of the emitter detectorpairs is positioned along a center line that it shares with the ballsupport 205. The other two of the emitter/detector pairs are equallyspaced on either side of the middle emitter/detector pairs. Among otherfunctions, this group of sensors 204 a operates as a “trigger” for theremaining sensors, applying power to the emitters of the remainingsensors only when a trigger event, indicating the passage of a golf clubhead, has occurred. A linear array of eleven emitters and ten detectors204 b is positioned transverse to the golf club swing path approximately1.25 inches closer to the golf ball support 205 than the trigger arrayof sensors 204 a. This array 204 b is the entrance row of sensors.Angled sensor array 204 c is arranged with two pairs of emitters anddetectors, each pair parallel to the major axis of the housing 200, witha pair aligned to either side of the ball support 205. In anillustrative embodiment the angled emitter detectors are positioned atan angle of 30 degrees with the upper surface 202 a of the housing 200.Such and alignment permits a system in accordance with the principles ofthe present invention to determine the height of a club head as itpasses overhead. The array 204 d of four emitters and five detectors ispositioned transverse to the club swing path approximately four inchescloser to the ball support than the trigger array 204 a. This, thecontact row of sensors, is positioned close enough to the ball support205 to detect club swing information coincident with, or just before,contact between a club face and the golf ball. That is, being within 1.5inches of the support 205 in the illustrative embodiment, the trailingedge of the retrorflective strip passes over the array substantiallyconcurrent with the time the ball is being struck and, consequently,data related from that array is data at the time of impact. Anotherangled sensors array 204 e is arranged with two pairs of emitters anddetectors, each pair parallel to the major axis of the housing 200, witha pair aligned to either side of and equidistant from the major axisthat passes through the center of the ball support. Additionally, inthis illustrative embodiment, the angled arrays 204 c and 204 e arepositioned an equal distance, d, of approximately three and one halfinches to either side of the ball support 205 and perpendicular to themajor axis of the housing 200. An exit row of sensors 204 f includeseleven emitters and ten detectors arranged transverse to the club swingpath 216 and a distance d2 approximately four and one half inches fromthe ball support 205 (that is, approximately the same distance from, buton the opposite side of, the ball support as the sensor array 204 b). Inthis illustrative embodiment, a signal light in the form of an LED 204 gis positioned in close proximity to the center of the threeemitter/detector pairs that form the sensor array 204 a. This embodimentof a sports swing analysis system employs the LED to indicate to a userwhether the user is operating in a “putting” mode or not.

The schematic representations of FIGS. 5 a, 5 b, and 5 c illustrate ingreater detail the operation of “angled arrays” 204 c and 204 e. The“ray tracing” representations of FIGS. 5 a and 5 b contrast thereflection from an “ordinary reflector” (FIG. 5 a) with reflection froma retroreflector (FIG. 5 b) as employed in this illustrative embodiment.In FIG. 5 a a ray of light emitted by emitter e travels along a path P1toward reflector R and is reflected in the familiar “angle of incidenceequals angle of reflection” mode along path P2. In this representation adetector D has an acceptance angle θ which precludes the detection oflight traveling along the reflected path P2. If detector D and emitter Ewere employed as one of the angled emitter/detector pairs of arrays 204c and 204 e and the reflector R were employed as the reflective materialcoupled to the club head 211, light emitted by the emitter E would notbe detected by the detector D as the club head 211 passed over the pairalong the path 216.

In contrast, the ray tracing of FIG. 5 b illustrates the use of aretroreflective material, as previously described. In this illustrativeexample, light emitted by the emitter E travels along the path P1 to thesurface of the retroreflective material RET where it is reflected alongthe path P2. Because the retroreflective material does not reflect lightaccording to the “angle of incidence equals the angle of reflection”,but, rather, along a path P2 much closer to the original path P1, adetector having the same acceptance angle, θ, (or an even narroweracceptance angle), will, in this instance, receive the reflected lightas the club head passes over the detectors along the path 216.

The side schematic representation of FIG. 5 c depicts the use of aretroreflective strip in concert with angled emitter/detector pairs todetermine the height of a golf club head above the top surface 202 a ofthe housing 202. Detector/emitter arrays 204 a-204 f are as previouslydescribed. A vertical broken line 500 represents the centerline of lightemitted from the emitters 204 be. As the golf club 210 passes over thearray 204 b, light emitted from the array strikes the bottom of the golfclub's head. As the club proceeds along the path 216 emitted light willstrike absorbent material for some period of time, then retrorefectivematerial, then absorbent material. That is, if the entire bottom surfaceof the golf club is covered by a light absorbent material, such as thedark electrical tape described, as previously described, with a strip ofretroreflective material applied over the tape, black tape will passover the array 204 b, followed by the retroreflective material, which isthen followed by more black tape. The same sequence of absorbent,reflective, and absorbent material will apply to the angled array 204 c.The light amplitude pattern of dark, light, dark, received at thedetectors is employed by the system to recognize the passage of a golfclub head and to distinguish such a passage from ambient light, thepassage of shadows, and other spurious events.

In one aspect of a system in accordance with the principles of thepresent invention, if the width of the reflective strip 212 and theheight of the strip are known, the system may determine the speed of theclub head by dividing the time required for the passage of the stripinto the width of the strip. That is, given a pair of light amplitudetransitions that represent the passage of the leading and trailing edgesof the reflective strip, the system divides width of the strip by thetime between the transition pair. A secondary correction can be made tocorrect for the spreading of the beams with distance, since the heightis known. In an illustrative example, the width of the strip is 0.25inches and the system treats club head speeds between 10 mph and 220 mph(corresponding, respectively, to 1420 microsecond and 64.6 microsecondintervals between leading and trailing edges) as valid speeds. That is,the apparent club head speed is used, in conjunction with otherparameter values, to determine whether variations in light amplitudereceived at the detectors are the result of emitted light beingreflected by a club head as it passes over the sensor arrays, or thevariations are due to other, extraneous, processes. Other, slower,speeds may be denominated valid in a putting mode, for example.

The system may record the time required for the club head to pass fromabove the array 204 b until the club head intersects with the path P1 oflight emitted from the angled array 204 c. Because the club head speedhas already been determined (that is, by dividing the width of the strip212 by the time between light level transitions corresponding to thepassage of the leading and trailing edges of the strip 212), thedistance D1 between the points of intersection of the club head with thevertical line from the array 204 b and the angled line P1 from theangled array 204 c may be determined by the system by multiplying thetime between those points of intersection by the speed of the club head.By subtracting the distance D3 between the arrays 204 b and 204 c fromthe distance D1, the system determines the distance D2. Given the angleφ and the distance D2, the system may determine the height H. Suchmeasurements and corresponding height determinations may be made forboth the heel and toe of the club head, using, respectively, the arrayscloser and farther from the location of a golfer (this proximity of thesensor arrays will vary according to whether the user's stance isleft-handed or right-handed).

Turning now to FIG. 6, the signal generation and processing functionalblock 104 is discussed in greater detail. A controller 600, which may becomposed of electronic circuitry that includes a microprocessor ormicrocontroller, for example, provides drive signals for the systems'emitters through an emitter interface 602. Two or more emitters may becontrolled with the same signal so that, for example, the emitters inthe array 204 c may all be turned on and off at the same time. Thecontroller 600 also controls the operation of a mode indicator interace602, which, in this illustrative embodiment, controls the operation ofputting mode LED 204 g. A detector interface 606 receives signals fromthe various detectors and passes them along to a differentiator 608. Thedifferentiator 608 may be implemented in a variety of circuitconfigurations and may take the form of AC coupling of detector signalsfrom the detector interface 606 to comparator circuitry 610. Thecomparator circuitry 610 converts the differentiated detector signal todigital form for processing by the controller 600.

FIG. 7 illustrates the system architecture for a computer system 700 onwhich a portion of the invention may be implemented. The exemplarycomputer system of FIG. 7 is for descriptive purposes only. Although thedescription may refer to terms commonly used in describing particularcomputer systems, the description and concepts equally apply to othersystems, including systems having architectures dissimilar to FIG. 7.

Computer system 700 includes a central processing unit (CPU) 705, whichmay be implemented with a conventional microprocessor, a random accessmemory (RAM) 710 for temporary storage of information, and a read onlymemory (ROM) 715 for permanent storage of information. A memorycontroller 720 is provided for controlling RAM 710.

A bus 730 interconnects the components of computer system 700. A buscontroller 725 is provided for controlling bus 730. An interruptcontroller 735 is used for receiving and processing various interruptsignals from the system components.

Mass storage may be provided by diskette 742, CD ROM 747, or hard drive752. Data and software may be exchanged with computer system 700 viaremovable media such as diskette 742 and CD ROM 747. Diskette 742 isinsertable into diskette drive 741 which is, in turn, connected to bus730 by a controller 740. Similarly, CD ROM 747 is insertable into CD ROMdrive 746 which is, in turn, connected to bus 730 by controller 745.Hard disc 752 is part of a fixed disc drive 751 which is connected tobus 730 by controller 750.

User input to computer system 700 may be provided by a number ofdevices. For example, a keyboard 756 and mouse 757 are connected to bus730 by controller 755. An audio transducer 796, which may act as both amicrophone and a speaker, is connected to bus 730 by audio controller797, as illustrated. It will be obvious to those reasonably skilled inthe art that other input devices, such as a pen and/or tabloid may beconnected to bus 730 and an appropriate controller and software, asrequired. DMA controller 760 is provided for performing direct memoryaccess to RAM 710. A visual display is generated by video controller 765which controls video display 770. Computer system 700 also includes acommunications adaptor 790 which allows the system to be interconnectedto a local area network (LAN) or a wide area network (WAN),schematically illustrated by bus 791 and network 795. An input interface799 operates in conjunction with an input device 793 to permit a user tosend information, whether command and control, data, or other types ofinformation, to the system 700. The input device and interface may beany of a number of common interface devices, such as a joystick, atouch-pad, a touch-screen, a speech-recognition device, or other knowninput device.

Operation of computer system 700 is generally controlled and coordinatedby operating system software. The operating system controls allocationof system resources and performs tasks such as processing scheduling,memory management, networking, and I/O services, among things. Inparticular, an operating system resident in system memory and running onCPU 705 coordinates the operation of the other elements of computersystem 700. The present invention may be implemented with any number ofoperating systems, including commercially available operating systems.One or more applications, such may also run on the CPU 705. If theoperating system is a true multitasking operating system, multipleapplications may execute simultaneously. An interface controller 733 maybe employed, for example, to communicate with the controller 600.

The flow chart of FIG. 8 illustrates the basic processes of a swinganalysis system in accordance with the principles of the presentinvention. A portion of such processes may be implemented on a computersystem such as computer system 700 described in the discussion relatedto FIG. 7. The process begins in step 800 and proceeds from there tostep 802 where the system determines whether a trigger event hasoccurred. In an illustrative golf swing analysis embodiment, emittersassociated with entrance row sensors 204 a sensors are turned “on” allthe time the system is being used and other sensors remain off untilafter a trigger event occurs. An event that indicates the passage of agolf club head over the sensors is detected by the detection and signalprocessing systems, previously described. In this illustrativeembodiment, the detection of two light amplitude transitions,corresponding to the passage of the leading and trailing edges of aretroreflective strip coupled to a club head, qualifies as such atriggering event. In step 802 the computer system 700 (upon which theanalysis, control, and interface system 106 may be implemented) polls atrigger processing function to determine whether such an event hasoccurred. If no trigger event has occurred, the process proceeds to step803 where the system determines whether it is to continue and, if not,the process proceeds to end in step 816. The decision to end the processmay be made on the basis of user interaction or by virtue of theexhaustion of a process timeout clock, for example.

If a trigger event has occurred and been detected in step 802, theprocess proceeds to step 804 where data from the trigger event isgathered. In an illustrative embodiment, data is gathered by turning onall of the systems' sensors, sampling data from each of the sensors(that is, all the detectors in all the arrays, 204 a-204 f) for apredetermined period of time at a predetermined rate. Whenever there isa state change (that is, a change in a comparator output correspondingto a reflected light-level transition associated with the passage of aleading or trailing edge of a reflective strip), the system records thetime of the transition. Transition data (that is, time of transition andthe identity of the detector that experiences the transition) isaccumulated until the predetermined time has elapsed. In an illustrativeembodiment, the data accumulation time is determined by the timerequired for a club head to travel the distance from the entrance rowsensors 204 a to the exit row sensors 204 b. This “travel time” may beemployed by a system in accordance with the principles of the presentinvention in a variety of ways. For example, because the emittersassociated with every sensor array other than the trigger array areturned on only during this period, more power may be applied to theemitters than would be the case if they were constantly “scanning” forclub heads. That is, the minimum timing interval is not limited, as someconventional systems' is, by the need to turn off, or otherwise limitthe power supplied to emitters that are constantly scanning becausetheir systems have no trigger-detection capability. That is, suchconventional systems continuously pulse power to their emitters at arate that prevents the emitters from overheating; a system in accordancewith the principles of the present invention, because it only operatesthe emitters when an event of interest has been detected by a triggerevent, can operate the emitters at full power, without pulsing, for alength of time consonant with the passage of a club head over the sensorarrays. Not only does the system avoid cycling the emitters (that is,cycling the emitters on an off) during the time a club head is passingover the housing 200, and thereby increase the resolution of the system(that is, the number of data samples the system may be able to obtainfor a given period of time), operating at higher power levels providesmore certainty in distinguishing reflections of interest from extraneouslight. Additionally, by limiting the data accumulation time, the systemreinforces limits placed on the range of club head speeds it willanalyze.

In an illustrative embodiment, the predetermined time set foraccumulating data is 0.1 seconds. Because the distance between theentrance and exit rows of sensors is less than a foot, 0.1 secondsprovides for the accumulation of sensor data for any club speed ofinterest. That is, at club speeds of 220 mph and 10 mph, a club headwould cover the distance between entrance and exit row sensors in lessthan 0.0031 seconds and 0.0682 seconds, respectively. Consequently, 0.1seconds provides a safe margin of time to record data of interest whileallowing the emitters to operate at full power for a period of time thatis brief enough to insure their safe operation. Each of the sensorsdelivers its output to the controller 600. In an illustrative embodimentthe signal generation and processing 104 identifies the input associatedwith each sensor. Such identification may be implemented, for example,through use of multiplexing techniques, for example. The controller isalso configured to control operation of the sensors and to provideclocking information associated with received signals. In thisillustrative embodiment, the controller is configured to identify whichsensors have transmitted signals indicating the time of their actuationat a frequency of 100 kHz for a corresponding timing rate ofapproximately 0.00001 second intervals. In this illustrative embodiment,the controller is a PIC RISC microcontroller, available from Microchip,Inc.

Data files are fed from the controller to the computer via an interface,such as the interface controller 733 described in the discussion relatedto FIG. 7. The controller monitors the sensors for change in stateevents and creates data files containing sequences of change of stateevents, along with their associated timestamps. As used herein, a changein state event occurs whenever the leading or trailing edge of thereflective tape passes over a sensor device. Each file includes at leasta particular sensor device identifier, a status field, and a time ofactuation field. The sensor device identifier may be any sort ofidentifier recognizable by the program. The status field may be anON/OFF indication, for example, a “1” or a “0”, representing whether theparticular device was actuated during a swing. The time field is filledwith the time of actuation, as compared to the time of actuation ofother sensor devices (for example, the time from activation of a triggerdevice).

The computer is programmed to assess whether a sufficient number ofindividual sensor devices were activated fro the purpose of making aswing assessment. The required number is a programming option. If aninsufficient number has been filled, that may indicate that the swingpath was wild or incomplete and the analysis process is terminated andthe user advised accordingly. The analysis first determines whether apossible club head “image” has been detected on the entrance and exitrows. If both images are present, a preliminary club head speedcalculation is made, based on measured time and known distance betweenthe rows. If a sufficient number of fields have been filled, theanalysis process continues by determining whether data from the sensorsconfirm a minimum gross club head speed has been detected. That initialspeed calculation is preliminarily made by calculating the spacingdifferential between particular activated ones of the sensors anddividing that number by the time lapse between activation of suchsensors. The minimum club speed could be any value, such as ten mph, forexample, that helps to determine whether a legitimate swing hasoccurred. Alternatively, no minimum speed would be set for analyzingputting strokes. If that minimum speed has not been achieved, theanalysis is terminated and the user so advised. If the minimum speed hasbeen reached and a sufficient number of sensors have been actuated, afile is created from the temporary folders data for detail analysisrelated to swing characteristics.

After gathering data in step 804, the process proceeds to decision step806, where the system determines whether to proceed in putting mode.This decision is based upon the data gathered in step 804. In anillustrative embodiment, a club head that passes over the center triggerof the trigger row 204 a, then over a sensor at the extreme end of theentrance row and no other sensors, initiates the putting mode. If theputting mode is not activated, the process proceeds to step 808 wherethe data gathered in step 804 is examined to determine whether anytransitions were recorded in the detectors associated with the exit rowsensors 204 f. If transitions were recorded in the exit row, the processproceeds to step 810, where recorded data is forwarded for processing instep 811.

In step 811, the data is used to calculate various parameters related tothe mechanics of the swung club. In accordance with the principles ofthe present invention, those parameters may include: swing path angle,club head speed, club head angle, lateral alignment, club head height,loft angle, ball flight path, shot distance, ball spin, swing tempo,ball stroke location on the club face, club face angle, and theeffective club head speed. In an illustrative embodiment a swinganalysis system in accordance with the principles of the presentinvention employs a strip of retrorflective material attached to thehead of a golf club. Due to the properties of retroreflective material,previously described, the system's sensor response is substantiallyindependent of the angle of the bottom of a passing golf club head.Consequently, for example, club heads with convex bottoms, thereflective sensing of which would pose a problem if using conventionalreflective material, are readily sensed using retroreflective material.Similarly, although various stance errors on the part of a user (forexample, hands forward or back, standing too close or too far away fromthe ball) may cause the bottom of the club head to be other thanhorizontal, the use of retroreflective material allows the system tooperate well, since emitted light that strikes the surface of theretroreflective material is returned substantially along the path ittook from its source. The retroreflective material also allows the useof the narrowest possible emitter light beams and the narrowest possibledetector sensitivity area, the combination of which maximizes theprecision of the system's position measurements. As a result,time-stamped data corresponds exactly to the edges of the reflectivetape passing directly over the particular detector.

The system organizes “on” and “off” edges, corresponding with leadingand trailing edges of a retroreflective strip sensed by a particularsensor. Such on/off pairs are referred to as an “event.” The systemorganizes patterns of overlapping events in the sensor rows as “clubsignatures.” For example, if a club head were traveling at 100 mph,perfectly square, and along a path that is directly down the center ofthe housing, one “pattern of overlapping events” would be that the fivemiddle detectors in entrance row 204 b would all turn on atapproximately the same time and all would turn off approximately142×10⁻⁶ seconds later (assuming a 0.25 inch wide retroreflective stripand assuming negligible beam spread). In an illustrative embodiment inwhich all the emitters are turned on at a high power level for 0.1seconds in response to a trigger event and the corresponding detectoroutputs are sampled for that 0.1 second period at 10×10⁻⁶ secondintervals, a significant number (fourteen) of “on” samples should beobtained, thereby providing a high confidence level that the item beingdetected is, indeed a reflective strip of interest and not merelyartifact. Alternatively, the system may search for a threshold number(four or five, for example) of overlapping events occurring on theentrance and exit row sensors. That is, the system may verify good databy examining turn on/turn off pairs that occur at approximately the sametime within a plurality of detectors within the same sensor row anddetermining that those events having durations corresponding to anappropriate speed. Events within each row may also be compared withevents detected within a plurality of rows.

In this illustrative embodiment “events” (that is, turn on/turn offpairs) are stored, along with a detector identifier and timestamp. Bystoring only this transition-related data, the system requires a greatdeal less memory than it would if all the data collected from all thedetectors were stored. Additionally, the system can perform calculationsrelated to the detector data much more quickly if it operates on thestored transition-related data than it would if it had to operate on themuch more extensive “raw” data produced by all the detectors for anentire 0.1 second sampling period.

The system calculates the club face angle by associating the timedifference between detector transitions within a pattern of events. Forexample, if a club face is swung approximately 7.2 degrees open, the endof the reflective strip closer to the golfer will create a transition ina row of detectors while the other end of the reflective strip still hasapproximately 0.25 inches to go before reaching the row of detectors(assuming a 2 inch long reflective strip, arcsin 0.25/2.0=7.2 degrees)At a club head speed of 100 mph, the 0.25 inch offset corresponds to a142×10-6 delay between transition events associated with either end ofthe reflective strip. Similarly, a 7.2 degree closed club face wouldcreate the same delay, but with the end of the reflective strip fartherfrom the golfer passing over a row of detectors before the end closer tothe golfer.

In an illustrative embodiment the swing analysis system calculates theswing path angle, determining which detectors in which rows correspondto the path of the same reflective strip feature. For example, thesystem may determine which detector signal transitions in detectorarrays 204 b and 204 f correspond to reflections from the end of thereflective strip closest to the golfer, farthest from the golfer, or thesystem may “average” detector responses to approximate detectortransitions due to the passage of the center of the strip. Once a pathis determined, for example, the center of the strip took a course thatpassed over a detector at one extreme of the array 204 b to the otherextreme of the array 204 f. In this illustrative embodiment, thatcorresponds to a movement across the housing of approximately 4.5 inchesin the course of transiting the nine inches between arrays 204 b and 204f. The system calculates the path angle as the arctan of 4.5/9, or, 26.6degrees. This value would be associated with a path attribute ofinside/out or outside/in, depending upon whether the club head traveled,respectively, from a point closer to the golfer to a point farther fromthe golfer or from a point farther from the golfer to a point closer tothe golfer.

In an illustrative embodiment, the swing analysis system calculates theclub head speed by determining the “event duration” (that is, the timebetween a turn on and a turn off transition). This event time could beassociated with detectors in the trigger row 204 a, for example. Aspreviously noted, if the width of the retroreflective material is known,the system can calculate the club head speed as the material widthdivided by the event duration. Additionally, the system may calculatethe club head speed as the distance between any two sets of arraysdivided by the corresponding delay between events. The system may makealso employ averaging and/or smoothing algorithms to better approximatethe club head speed. Because the system determines overlapping eventscorresponding to club signatures on all sensor rows, the system mayemploy data (that is, timestamps and detector identifications)associated with those signature events to determine speed, path angle,etc. The system may set acceptable timing and event duration ranges, anddiscard data associated with out-of-limits edge detection. This allowsthe system to “filter out” spurious data. The process of searching outpatterns of overlapping events and discarding out-of-limits data may berepeated until, for example, the calculated results fall within apredetermined confidence level. In effect, a system in accordance withthe principles of the present invention sets a window for the mostlikely duration of valid events for a given club head speed. If thespeed and duration don't match, extreme events are discarded and thesystem recalculates the speed and duration of the remaining events untilthe system has identified swing events that fit within the norm, or,until all the collected events are discarded.

A system in accordance with the principles of the present invention mayemploy the club head speed and face angle to compute the ball spin,triangulation techniques such as previously described to compute a clubhead's toe and heel height before and after impact with a ball. The shotdistance may calculated based on the club selection, club head speed,swing path, face angle, and point of contact on the club face. A ball'slanding spot may be calculated on the basis of ball flight distance,spin, and the simulated course's terrain. In an illustrative embodiment,a golfer's tempo is the time between his backswing and downswing. Aclub's lateral alignment is determined by drawing an imaginary line fromthe club center at the entrance row to the club center at the exit row.The effective club head speed is determined, in this illustrativeexample, by derating the club head speed according to the degree towhich the club face angle was off-square at the point of impact.

From step 811, the process proceeds to step 812, where the results ofthe calculations are displayed. In addition to displaying results of thecalculations, the system may provide audio feedback and may provide avariety of display modes. Such audio feedback may be employed by a userto be coached while concentrating on the ball, his stance, hismechanics, without looking at a display, for example. From step 812 theprocess proceeds to step 814 where the system decides whether tocontinue or not. This decision may be based upon user input or a systemtimeout, for example. If the process is not to continue, it proceeds toend in step 816. If the process is to continue, the process returns tostep 802 and, from there, as previously described.

If, in step 808, the process determines that there had been no eventsassociated with sensors in the exit row, the system concludes that thetrigger event of step 802 is associated with a player's backswing motionand the process proceeds to step 818. In step 818 backswing datarecorded in step 804 is sent to the calculation process of step 819. Instep 819 the swing analysis system employs the time between twosequential trigger events, associated with a club head passing over thetrigger array 204 a in a reverse direction, followed by it's passage inthe forward direction, to calculate the player's backswing tempo. Aftercalculating the backswing parameters in step 819, the process proceedsto step 812, where the backswing information is displayed, and, fromthere, the process proceeds as previously described.

Returning to step 806, if the system determines that a player's inputindicates a desire to operate the system in the putting mode, theprocess proceeds to step 820. In step 820 the system gathers swinganalysis data related to putting. Because putting is considerablydifferent from a “regular” swing (that is, a tee shot, or chip shot, forexample) the process of gathering data related to a player's puttingstroke is also considerably different. For example, the expectedclubhead speed is much slower than that associated with a regular swing.Consequently, the putting data-gathering process takes place on a muchslower time scale.

In an illustrative embodiment, once the putting mode is entered, thesystem temporarily stores the state [that is, “on” (detecting light), or“off” (not detecting light)] of all the detectors in all the sensorarrays 204 a-204 f. Then, all the emitters in all the sensor arrays areturned on and the state of all the detectors in the sensor arrays isonce again temporarily stored. All the emitters are then turned off, andthe most recently stored state information for each of the detectors iscompared to the corresponding next-most recently stored state in orderto determine which, if any, of the detectors has undergone a change instate. The system timestamps each change of state for each detector inwhich a change of state is detected. The process of turning all theemitters on, logging the state of each detector, and timestamping eachchange of state continues until the end of the putting process. The endof the process may be brought about by virtue of user interaction or bya timeout, for example. In this illustrative embodiment, the pulsing ofemitters in the putting mode takes place over an extended period of timein order to allow for the relatively slow strokes related to putting. Inthe putting mode, light level transitions are associated, not with thepassage of the leading and trailing edges of a reflective strip, as inthe normal mode of operation, but with reflections from a reflectivestrip associated with the pulsing on and pulsing off of emitters.

The system employs the timestamp list, as it does in other modes ofoperation, to determine the motion of the club head. That is, aspreviously described, a system in accordance with the principles of thepresent invention computes the values of various club head parameters,such as path angle, by examining the sequential detection of club headfeatures at sequential detector locations. In this illustrativeembodiment, those sequential detections are stored in the form of atimestamp list. After gathering the putting data in step 820, theprocess proceeds to step 822 where the data is forwarded to thecalculation process of step 823. In step 823 the values of puttingparameters are calculated, then the process proceeds to step 812, wherethose values are displayed. From step 812, the process proceeds aspreviously described.

The computer is programmed to determine the swing path angle, club headspeed, club head angle, club head lateral alignment, and club head toeand heel height before and after impact and the club head loft. Thisinformation also enables the system to calculate the ball strikelocation on the club face. In addtion, the effective club head speed maybe calculated. This rating is calculated based on the ratio of the clubhead angle, the relation of the club head to center, and the swing pathto those parameters for an idealized swing and multiplying that fractionby the measured club head speed to obtain an overall or composite swingrating. Furthermore, based on this information, the systems calculatesinformation about the shot that would have been taken if a real golfball had been hit by the swing. Such information calculated includes theflight path of the ball, the distance of the shot, the spin of the balland the swing tempo. This information enables the system to generate athree-dimensional representation of the shot, which can then besuperimposed on a representation of a golf hole stored in the memory ofthe computer. The system is able to apply the calculated information toa standard golf hole, to a driving range simulation, and to a practiceputting green simulation, as described in greater detail in thediscussion related to the following Figures.

The calculated values may be displayed as textual information, a simplegraphic representation, a multimedia representation, or any combinationthereof on the display computer device. The computer may, optionally, beprogrammed to retrieve historical swing information associated with thecurrent user, another user who has used the system or another player,such as a professional player or an “idealized” player swing attributeshave been stored on the computer for comparison purposes. The system maybe employed to analyze a player on a swing-by-swing basis, with swinganalysis data cleared after each shot, or the swing information may betied to a computer representation of a game simulation. The swinginformation captured by the system may be integrated into a courserepresentation.

Such simulations are shown in FIGS. 9, 10, and 11. FIG. 9 is a screenshot 900 of one hole of a 3-D golf course that the user may play usingthe simulations calculated by the system 100. The screen includes therepresentation of the hole as well as a window which displays theinformation calculated by the system for each shot taken by the user.Other displays permit the representation of the hole being played and awindow showing a representation of the shot as seen from above and awindow showing the shot as seen from ground level. All of the datacalculated by the system may be represented either in text on the screenor in pictures that show the shot in windows. The screen shot 900illustrates data presentation such as may displayed by a swing analysissystem in accordance with the principles of the present invention. In anillustrative embodiment, the system operates in five display modes:Practice Range, Practice Course, Practice Green, Course Game, and GreenGame. The Practice Green and Green Game display modes operate inconjunction with the putting mode of data capture and analysis, asdescribed in the discussion related to FIG. 8. The Practice Range,Practice Course, and Course Game display modes operate in conjunctionwith the regular swing mode of data capture and analysis, as describedin greater detail in the discussion related to FIG. 8. Toolbar buttons902, 904, 906, and 908 allow a user to, respectively, select the mode ofplay, select the club to use for analysis, select the view to bedisplayed, and select other options. In this illustrative example,information obtained by the system's sensor arrays and conditioned andanalyzed by the controller has been passed to the computer for display.This particular display simulates a driving range and the visualfeedback is organized in four windows. The largest window 910 includesgraphical information that portrays the layout of a driving range, withyard markers 912, and a trace 914 that indicates the ball's trajectory.

A box 916 in the upper left corner of the window 910 includes textualinformation regarding a swing that has been analyzed by the system. Thisinformation includes the distance the ball has traveled (that is, thedistance a ball would have traveled according to the simulationconducted by the system based on the information obtained from thesensor arrays and controller), in this cases 214.1 yards. The box alsolists the speed at which the ball traveled, 74.9 mph, the swing tempo,0.9 seconds (that is the time of a user's backswing), left or right ofcenter, 4.2 yards (the distance at which the ball landed to the left orright of the user's intended ball path), and the toe and heel heights ofthe club relative to the “ground” (that is, to the upper surface of thesensor housing). The toe and heel heights indicate whether the club wasangled in the vertical plane when the retroreflective strip intersectedthe beams of the angled arrays, as described previously described. TheIN values are the heights of the club head toe and heel before ballcontact (related to measurements from arrays 204 c) and the OUT valuesare the heights of the club toe and heel after ball contact (related tomeasurements from arrays 204 e). The “Penalty” value displayed at thebottom of the box 916 is computed by the system to reflect a combinationof factors, including how far outside the club's sweet spot the ball wasstruck and the terrain on the course (for example, whether the ball wasbeing hit from the rough).

A window 918 displays textual and graphical information regarding theswing's face angle and swing path. The system computes and displays theclub's face angle before, after, and at the point of contact with theball. Data relating to these positions are primarily obtained from theentrance 204 b, contact 204 d, and exit row 204 f sensors, respectively,as previously described. The face angle is given in degrees, along withan indication of whether it is open, closed or square (that is, the faceangle is zero). A square club face is desired for most shots. If a useris right handed and the face angle is open on contact, the face of theclub is perpendicular to a line point to the right of the desired lineof flight of the ball. If the face angle is closed, the face is pointingto a line pointing to the left of the desired line of flight of theball. The IN/OUT swing path is also given in degrees and is the path ofthe club across the sensor unit 200. A square swing angle cuts a pathdirectly across the middle of the swing sensor unit. For a right-handedgolfer, an inside out swing describes a path from the lower right handcorner to the upper left hand corner in the window 918 and an outside inswing path follows a path from the upper right to the lower left handcorner of the window 918. This illustrative system displays a confidencemeter 919 in the window 918 to indicate to a user the degree ofconfidence the system has in its calculations. The system's confidencein its measurements and calculations may be affected by lightinterfering with the sensors or errant swings, for example, and themeter 919 provides the system with a way in which to apprise a user ofthe system's view of the reliability of its current measurements.

The window 920 displays, in both textual and graphical form, ameasurement (in degrees) of a swing path's variation, at the point ofimpact with the ball, from an imaginary horizontal plane (that is, aplane parallel to the plane of the top of the sensor housing. The window920 also displays a plurality of club head heights. In this illustrativeexample, the displayed club head heights are measured as the clubapproaches the ball (0.9 inches), at the point of impact with the ball(0.2 inches), and after impact with the ball (0.4 inches). The window924 displays information related to the location on the clubface atwhich the ball was struck. In a graphical component of the display, ared cross marks the impact point on the clubface and a textual displayindicates the distance between the impact point and the club's sweetspot. The sweet spot is the ideal contact point on the club face, thecontact point that yields maximum distance and power. The in thisillustrative embodiment, penalties may be assigned to the trajectory ofa ball corresponding to the distance between the actual point of impactand the desired point of impact (that is, the sweet spot). The format ofthe information displayed in this screen shot may be used, with minormodification, in a number of the system's modes of operation. That is,it may be used in conjunction with the Practice Range, Practice Course,and Course Game modes, with minor modifications, such as changes to theterrain and elimination of yard markers 912 in the Practice Course andCourse Game modes.

In an alternative mode of operation, the system may be used to monitor aputting stroke. Since a golfer, when lining up a put, may take severalpractice swings, the system must be able to distinguish the practiceswings from the actual putting stroke. In an illustrative embodiment,the system is placed in a putting mode by swinging a putter diagonallyacross arrays 204 a and 204 b. The system then begins storinginformation received by the sensors in a circular buffer for apredetermined period of time: ten seconds, for example. Since theputting swings are much slower than a regular swing, the system, inputting mode, operates at a lower power for a greater period of timecompared to the standard swing mode described above. The system takesthe last set of data stored in the circular buffer and analyzes it togive the calculated information for the put stroke.

The screen shot of FIG. 10 is of a display that provides substantiallythe same information as the screen shot of FIG. 9, except that thisscreen shot relates to data collected and analyzed while the system isoperated in its putting mode. The illustrative embodiment's putting modedata gathering and analysis operations may provide data for the PracticeGreen and Green Game display modes. The box 916 provides a listing ofthe same type of information, as do windows 918, 920, and 924. The trace914 provides an indication of the balls trajectory that, unlike that ofFIG. 9, remains in contact with the ground. A box 1000 indicates the layof the terrain and the distance to the hole. A system in accordance withthe principles of the present invention may provide a plurality ofgreens for user interaction. In this illustrative embodiment, thePractice Green mode provides user interaction for nine different greens,with each green featuring different putting lengths. The system may beused to train a user to execute straight putts. The system's userinterface allows a user to line up his sight for a putt. Depending uponthe green and the lie of the ball, the ideal stroke may be in a directline to the hole, to the right of the hole or to the left of the hole.In response to data collected and processed by the sensor arrays, thecomputes the trajectory of the user's shot, allowing for the slope ofthe green, and the accuracy and power of the user's shot. Based on thefeedback displayed as in FIG. 10, a user may modify his stance and swingin order to hit the ball with a square swing path, a square club face,and with the sweet spot of the club.

FIG. 11 is screen shot of a course overview available with the PracticeCourse and Course Game modes of the system's operation. In thisillustrative embodiment, a user may select from a variety of teelocations (e.g., pro, intermediate, beginner, or women's tees), types ofplay, and other options. During a game, players may start in a numericalsequence (e.g., 1,2,3, and 4) and, on subsequent holes, the system willautomatically determine the order of shooting, based on the distanceeach shot lies from the hole being played. The user interface is alsoconfigured to allow a player to take a “Mulligan” and “whiff.” If aplayer hits a ball out-of-bounds, the player will be assessed a penaltystroke and the ball will automatically be placed on the fairway at thepoint where it crossed out of bounds.

In addition to the several views available corresponding to shot typeand analysis, the system allows a user to choose from various viewsrelated to the travel of the ball, and these views are available in aplurality of modes. In particular, a user may choose, “still”, “followthe ball”, or “spin” views. In the “still” view, the user observes theball trajectory from a stationary viewpoint corresponding to the placewhere he was standing when he hit the ball. In the “follow the ball”view, the user's viewpoint follows the ball, as thought tethered to theball. And, in the “spin” view, the viewpoint follows the ball and thenspins to a side view that travels along with the ball. The system's userinterface also allows a user to “fly over” the course at any time. A flyover generates a “fly thru” of one or more holes from the respective teebox to hole pin. In accordance with the principles of the presentinvention, the system creates a three-dimensional (3D) representation ofthe course upon which a user is playing and, as a result, the views justdescribed, which relate the flight of a user's golf ball to a 3D virtualgolf course are available to a user. The creation of the 3D virtualcourse and the ball-related views may be implemented using animation andrendering techniques known in the art.

The system allows a user to interact, through a keyboard or a mouse, forexample, with the user interface to thereby move the viewpoint of thefly thru up or down in order to get a better view of the hole. The userinterface also allows a player to drop a ball anywhere on the course inorder to practice shots from the selected location. The allows playersto call up previous shots and to thereby allow a player to review thestored shots, to compare the shots, and to review the progress he may bemaking. A user may select wood and iron tee heights (heights usedwhenever a shot is hit with a driver or wood, or with an iron), andgrass height (the height used whenever the player hits from the grasswith an un-teed ball. This height information will be used by the systemin conjunction with data collected from the sensor arrays to determinethe location on the club face that strikes a ball when the player takesa shot. At the option of a user, the system may align the putt directionto a “hint line”, allowing a user to get a feel for how to play the layof a putt.

The system provides audio feedback which a user might employ duringpractice to obtain feedback while focusing on his shots. That is, a usermay select a mode that announces the data and swing analysis, such as isdisplayed in the various display windows previously discussed. Byannouncing the data through use of a speaker, such as speaker 770, auser may, for example, take a shot, hear the analysis of the shot, andline up his next shot, all while focusing on his ball and club, withoutresorting to viewing the system's display output.

The perspective view of FIG. 12 a is a more detailed view of a mat 215that may be employed in a swing analysis system in accordance with theprinciples of the present invention. In this illustrative embodiment,the mat 215 includes top and bottom layers 1202 and 1204, respectively.The top layer 1202 is composed of a resilient material, such as auniback simulated grass surface, available from Grass-Tex, Inc., DaltonGa. that emulates the texture and appearance of grass. Both layers aremade of durable resilient materials. The bottom layer may be made of anEVA foam, available from Der-Tex, Saco Me. The thickness of the mat T,is selected to be approximately the same thickness as that of the sensorhousing, thereby supporting a user at approximately the same level asthe top surface of the sensor housing. The head 1208 and foot 1210 ofthe mat are associated with the ends of the sensor housing that include,respectively, the exit and entrance row sensors. The drawing is not toscale. An aperture 1206 is designed to receive the sensor housing 202.Because the mat is made of resilient flexible materials, it may befolded or rolled for convenient packaging and transportation. FIG. 12 bprovides a sectional view from the foot 1210 of the mat 215. In thisillustrative embodiment, the top layer 1202 includes three sections1212, 1214, and 1216, that extend the length of the mat, from head tofoot. The sections 1212, 1214, and 1216, are coupled to the bottom layer1202, in an illustrative embodiment, by an adhesive such as a heat-curedadhesive. Adhesive-free voids 1218, and 1220 are left on either side ofthe top section edges that form joints between top sections 1212 and1214 and between top sections 1214 and 1216. The adhesive voids run thelength of the mat 215. In this illustrative embodiment, the combinationof adhesive voids 1218 and 1220, flexible, resilient materials used fortop 1202 and bottom 1204 layers, and the three-section composition ofthe top layer 1202, permit the mat 215 to be readily folded “in three”for packaging and transportation, along the joints formed between topsections 1212 and 1214 and between top sections 1214 and 1216.

A software implementation of the above described embodiment(s) maycomprise a series of computer instructions either fixed on a tangiblemedium, such as a computer readable media, e.g. diskette 742, CD-ROM747, ROM 715, or fixed disc 752 of FIG. 2, or transmittable to acomputer system, via a modem or other interface device, such ascommunications adapter 790 connected to the network 795 over a medium791. Medium 791 can be either a tangible medium, including but notlimited to, optical or analog communications lines, or may beimplemented with wireless techniques, including but not limited tomicrowave, infrared or other transmission techniques. The series ofcomputer instructions embodies all or part of the functionalitypreviously described herein with respect to the invention. Those skilledin the art will appreciate that such computer instructions can bewritten in a number of programming languages for use with many computerarchitectures or operating systems. Further, such instructions may bestored using any memory technology, present or future, including, butnot limited to, semiconductor, magnetic, optical or other memorydevices, or transmitted using any communications technology, present orfuture, including but not limited to optical, infrared, microwave, orother transmission technologies. It is contemplated that such a computerprogram product may be distributed as a removable media withaccompanying printed or electronic documentation, e.g., shrink wrappedsoftware, preloaded with a computer system, e.g., on system ROM or fixeddisc, or distributed from a server or electronic bulletin board over anetwork, e.g., the Internet or World Wide Web.

Although various exemplary embodiments of the invention have beendisclosed, it will be apparent to those skilled in the art that variouschanges and modifications can be made which will achieve some of theadvantages of the invention without departing from the spirit and scopeof the invention. It will be obvious to those reasonably skilled in theart that other components performing the same functions may be suitablysubstituted. Further, the methods of the invention may be achieved ineither all software implementations, using the appropriate object orprocessor instructions, or in hybrid implementations that utilize acombination of hardware logic, software logic and/or firmware to achievethe same results. The specific configuration of logic and/orinstructions utilized to achieve a particular function, as well as othermodifications to the inventive concept are intended to be covered by theappended claims.

The foregoing description of specific embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseforms disclosed, and many modifications and variations are possible inlight of the above teachings. The embodiments were chosen and describedto best explain the principles of the invention and its practicalapplication, and to thereby enable others skilled in the art to bestutilize the invention. It is intended that the scope of the invention belimited only by the claims appended hereto.

1. An apparatus comprising: a sports implement for swinging; and aretroreflective strip coupled thereto for providing a distinctreflection pattern from one or more surfaces of the implement.
 2. Theapparatus of claim 1 wherein the sports implement is a baseball bat. 3.The apparatus of claim 1 wherein the sports implement is a tennisracquet.
 4. The apparatus of claim 1 wherein the sports implement is agolf club.
 5. The apparatus of claim 4 further comprising: alight-absorbent material coupled to the implement to form at least onelight reflection transition region between the light absorbent andretroreflective materials.
 6. The apparatus of claim 1 wherein theimplement comprises a receptacle for receiving the retroreflectivematerial.
 7. The apparatus of claim 6 wherein the implement is abaseball bat.
 8. The apparatus of claim 6 wherein the implement is atennis racquet.
 9. The apparatus of claim 6 wherein the implement is agolf club.
 10. The apparatus of claim 9 further comprising: alight-absorbent material coupled to the golf club to form at least onelight reflection transition region between the light absorbent andretroreflective materials.
 11. The apparatus of claim 10 wherein thelight absorbent and retroreflective materials are coupled to the head ofthe golf club via adhesive.
 12. The apparatus of claim 11 wherein theretroreflective material is a strip of predetermined width.
 13. Theapparatus of claim 12 wherein the retroreflective material is coupled tothe implement in a predetermined orientation.
 14. The apparatus of claim12 wherein the receptacle is an indentation on the head of the golfclub.
 15. A method of preparing a sports swing implement for analysiscomprising the steps of: (A) producing the sports swing implement; and(B) applying retroreflective material to a surface of a sportsimplement.
 16. The method of claim 15 wherein the step (B) of applying aretroreflective material comprises the step of: (B1) applyingretroreflective material to a surface of a golf club.
 17. The method ofclaim 16 wherein the step (B) of applying retrorefelctive materialcomprises the step of: (B2) applying a strip of predetermined width. 18.The method of claim 16 wherein the step (B) of applying retrorefelctivematerial comprises the step of: (B3) applying a strip in a predeterminedorientation.
 19. The method of claim 16 wherein the step (B) of applyingretrorefelctive material comprises the step of: (B4) applying lightabsorbent material to form at least one light reflection transitionregion between the light absorbent and retroreflective materials. 20.The method of claim 16 wherein the step (A) of producing the implementcomprises the step of: (A1) forming a receptacle in the implement toreceive retroreflective material.